Since the development of the integrated circuit there has been a constant increase in the speed of electronic signals brought on by the continuous increases in transistor density in semiconductor process. While the needs of electronic signals were successfully handled by traditional methods of IC packaging and interconnection for most of the history that followed the introduction of the IC, beginning in the late 1990s it was becoming increasingly clear that traditional approaches would reach a point where they could no longer deliver the performance needs of the signal. Today, semiconductor technology has finally pushed the limits of traditional IC packaging, printed boards and connector technology to the point where the current construction techniques can no longer provide adequate signal quality.
For current and foreseeable future generations of electronic systems, controlling signal loss and the impedance of signal traces has become the key area of focus for the electronic system designer intent on transmitting electrical signals in the gigahertz range. The approach to date for IC chip packaging and printed circuit board design to address the problem has been to make incremental changes in material choice and design and supplement those choices with sophisticated semiconductor electronics that pre and/or post emphasize the signal and to employ higher power to overcome the losses associated with the parasitic effects of present design and manufacturing practices. To gage the size of the gap, one can look at current generation IC microprocessors which are operating at near 4 gigahertz while the PCB bus which serves them operate at only 800 MHz.
Included among those features that can have deleterious effects are abrupt transitions and features such as plated vias which alter the capacitance in mid run creating signal discontinuities and their stubs which cause reflections and electronic noise. Thus plated vias, solder balls and trace transitions between layers all introduce deleterious impedance changes resulting in poor signal quality. This limits overall signal speed.
While their have been attempts to minimize the parasitic effects of circuit design elements, adjustments so far have yielded only marginal benefit and there is opportunity and need to improve on current design and manufacturing approach to meet the pending demand for a significant magnitude leap in performance required for next generation electronic systems. However, if one can eliminate or severely limit or mitigate the use of vias, solder balls and trace transitions, a printed circuit board is capable of supporting much higher signal speeds with less signal degradation.